Mechanical properties of bidimensional T-loop closing springs compared with conventional T-loops: A 3-dimensional...

T-loop closing springs are widely used for extraction space closure in friction-free orthodontic mechanics. The bidimensional technique exploits differential wire-slot engagement to enhance anterior torque control; however, its application to T-loop design has not been investigated. This study aimed to compare the 3-dimensional force systems produced by conventional and bidimensional T-loop closing springs across different interbracket distances and activation levels using finite element analysis.

Six 3-dimensional T-loop models were constructed using SolidWorks 2021 (Dassault Systèmes, Vélizy-Villacoublay, France): 3 conventional and 3 bidimensional designs made from 0.016 × 0.022-in stainless steel wire, each modeled at interbracket distances of 6, 8, and 10 mm. All models assumed a 0.022-in bracket slot. The bidimensional variant incorporated a 90° torsion bend at the loop's midportion. Static structural analysis was performed in ANSYS 2021 R2 (ANSYS Inc, Canonsburg, Pa) with cinch-back activations of 2 mm and 4 mm. Digital sensor probes recorded forces and moments at both wire ends along 3 spatial axes.

Bidimensional T-loops consistently generated higher horizontal forces and moments than conventional designs. With 2-mm activation at a 6-mm interbracket distance, the alpha-end horizontal force was 3.29 N in the bidimensional design compared with 2.52 N in the conventional design (∼30% increase). Alpha-end moment-to-force ratios ranged from 4.14-5.58 mm for the bidimensional design vs 3.95-5.11 mm for the conventional design. The 90° torsion bend reduced alpha bracket-slot angular clearance from 3.8° to 0.95°.

Based on theoretical finite element predictions, the bidimensional T-loop design produces greater forces, moments, and alpha-end moment-to-force ratios than conventional T-loops. Reduced alpha-end bracket-slot play may reduce moment attenuation, offering potential biomechanical advantages for maximum-anchorage retraction. These are theoretical mechanical predictions that require clinical and experimental validation before definitive conclusions can be drawn.